Electrical leads having a low electrical resistance as a rule also exhibit low thermal resistance. When an electrical lead is passed through a thermal insulator, a thermally insulating substance having a low thermal conductivity is interrupted at least in single-point fashion by the electrical lead having a high thermal conductivity, so that a thermal bridge is produced. The larger the conductive cross section of the electrical lead, the greater the heat loss via a thermal bridge of this kind. The problem of undesired heat loss or heat exchange thus increases as the conductive cross section increases. In cases in which a large conductive cross section is necessary so that high electrical currents can be transported, a large heat loss can also be expected. As soon as a thermal difference exists between the sides of a thermal insulator, a thermal flux occurs and is reflected in a heat loss, regardless of whether an electrical current is flowing.
One example of such a situation is represented by the operation of a thermally insulated high-temperature battery. In batteries that are operated at temperatures above ambient temperature, such as LiS batteries having a polymer electrolyte, not only electrical energy but also energy in the form of heat flows out via the electrical lead. If the heat required for operation of the battery is generated by the battery itself, the energy required in order to compensate for the heat loss reduces the electrical energy that can be furnished to a load.
An energy loss of this kind cannot be avoided during usual discharge of the battery; if the conductive cross section is selected appropriately, the energy loss due to the heat flow is usually negligible as compared with the energy withdrawal by way of the electric current. If an electrical discharge is intermittently interrupted, however, as is the case e.g. in an electric vehicle, the energy loss due to the heat loss can result in a loss of several percent of battery capacity.
In order to reduce heat flows from electrical supply conductors in the region of an insulating sleeve of electrochemical units, German Patent Application No. DE 10321132A1 describes a disconnecting switch in the region of a passage through a heat absorber, by way of which the electrical connection can be interrupted and heat transport in the region of a supply conductor can be reduced.